temporal variants of generate_series()

I've written the following function definitions to extend
generate_series to support some temporal types (timestamptz, date and
time). Please include them if there's sufficient perceived need or
value.

-- timestamptz version
CREATE OR REPLACE FUNCTION generate_series
( start_ts timestamptz
, end_ts timestamptz
, step interval
) RETURNS SETOF timestamptz
AS $$
DECLARE
current_ts timestamptz := start_ts;
BEGIN
IF start_ts < end_ts AND step > INTERVAL '0 seconds' THEN
LOOP
IF current_ts > end_ts THEN
RETURN;
END IF;
RETURN NEXT current_ts;
current_ts := current_ts + step;
END LOOP;
ELSIF end_ts < start_ts AND step < INTERVAL '0 seconds' THEN
LOOP
IF current_ts < end_ts THEN
RETURN;
END IF;
RETURN NEXT current_ts;
current_ts := current_ts + step;
END LOOP;
END IF;
END;
$$ LANGUAGE plpgsql IMMUTABLE;

-- date version
CREATE OR REPLACE FUNCTION generate_series
( start_ts date
, end_ts date
, step interval
) RETURNS SETOF date
AS $$
DECLARE
current_ts date := start_ts;
BEGIN
IF start_ts < end_ts AND step > INTERVAL '0 seconds' THEN
LOOP
IF current_ts > end_ts THEN
RETURN;
END IF;
RETURN NEXT current_ts;
current_ts := current_ts + step;
END LOOP;
ELSIF end_ts < start_ts AND step < INTERVAL '0 seconds' THEN
LOOP
IF current_ts < end_ts THEN
RETURN;
END IF;
RETURN NEXT current_ts;
current_ts := current_ts + step;
END LOOP;
END IF;
END;
$$ LANGUAGE plpgsql IMMUTABLE;

-- time version
CREATE OR REPLACE FUNCTION generate_series
( start_ts time
, end_ts time
, step interval
) RETURNS SETOF time
AS $$
DECLARE
current_ts time := start_ts;
BEGIN
IF step > INTERVAL '0 seconds' THEN
LOOP -- handle wraparound first
IF current_ts < end_ts THEN
EXIT;
END IF;
RETURN NEXT current_ts;
current_ts := current_ts + step;
END LOOP;
LOOP
IF current_ts > end_ts THEN
RETURN;
END IF;
RETURN NEXT current_ts;
current_ts := current_ts + step;
END LOOP;
ELSIF step < INTERVAL '0 seconds' THEN
LOOP -- handle wraparound first
IF current_ts > end_ts THEN
EXIT;
END IF;
RETURN NEXT current_ts;
current_ts := current_ts + step;
END LOOP;
LOOP
IF current_ts < end_ts THEN
RETURN;
END IF;
RETURN NEXT current_ts;
current_ts := current_ts + step;
END LOOP;
END IF;
END;
$$ LANGUAGE plpgsql IMMUTABLE;